In situ Raman spectroscopic studies on the current oscillations during gold electrodissolution in HCl solution

Raman spectroscopy has been used for investigating the gold oscillatory electrodissolution processes in a 2 mol dm(-3) HCl solution. The vibration bands for Au-Cl-, AuCl4- and Au-O(H) as a function of potential, the spatial profile of AuCl4- concentration in the diffusion layer, and the temporal evolution of AuCl4- during the current oscillations have all been measured in situ by a confocal Raman spectroscope. These experimental results indicate that the transition between active and passive states of gold accounts for the current oscillations in a very narrow potential range. A crossing cycle in the cyclic voltammogram that means a pair of overlapping positive and negative feedbacks corresponds to the active-passive transition. A possible oscillatory electrodissolution mechanism has been proposed on the basis of the experimental results. (C) 2003 Published by Elsevier B.V.